Sympathetic cooling of trapped ions: A laser-cooled two-species nonneutral ion plasma

Sympathetic cooling of trapped ions has been demonstrated in an experiment where Hg+198 ions were confined in a Penning ion trap with laser-cooled Be+9 ions. Hg+198 temperatures below 1 K were achieved. Ion plasma sizes, shapes, and rotation frequencies were measured. Dramatic changes in the Be+9 plasma were observed when the Hg+198 ions were introduced into the trap. These observations are consistent with the prediction of centrifugal separation for ions of different charge-to-mass ratios.